Tire sealant had been used in tires for sealing punctured tire. There are two types of tire sealant that function under different occasions. The common one is usually injected to pneumatic tires after puncture is discovered. Normally, the sealant is injected to the tire through the valve stem by pressurized air. As sealant passes puncture holes, it blocks the holes and stops gas leakage. A sufficiently large volume of sealant is required. It is usually preformed as an emergency solution for tire puncture because the sealant degrades gradually.
Preventative sealant is another type of tire sealant. It is placed inside the tire before occasion of puncture and served as a precaution. When tire puncture occurs, the sealant, which keeps circulating inside the tire, passes and seals the puncture.
In either cases, it is unavoidable that a large amount of sealant is required resulting in an increase of vehicle loading and a reduction of capacity of vehicle. This is undesirable in current market which emphasizes environmental friendly and cost effective products. Therefore, sealant of high sealing performance with small volume is demanding.
Foam sealant capable in expansion in volume is an alternative. An example of this type of sealant is disclosed in U.S. Pat. No. US 2013/0072594 A1. It discloses a sealant formula comprised of reactive blowing agent. It demonstrates an expansion of sealant due to chemical reaction. Isocyanate group in one of the suggested blowing agents is toxic, and its median lethal dose (LD50) is 5,000 mg/kg. Another recommended blowing agent (carboxy groups and hydrogencarbonate salt) generates carbon dioxide during foaming. However, the tire sealant may be stored in car baggage compartment, which can be very hot, so this may induce thermal decomposition of hydrogencarbonate that releases CO2. This may result in the leakage of sealant or explosion of sealant container. Hence expansion of sealant shall not rely on chemical reaction. In addition, consumers may scare of a sealant comprising reactive chemical.